2 ipchains command ipchains -[ADC] chain rule-specification [options] ipchains -[RI] chain rulenum rule-specification [options] ipchains -D chain rulenum [options] ipchains -[LFZNX] [chain] [options] ipchains -P chain target [options] ipchains -M [ -L -S ] [options] -A <chain> ADD a rule to chain: input Input chain forward Forwarding chain output Output Chain -I <chain> Insert a new rule at some position in a chain -R <chain> Replace a rule at some position in a chain -F [<chain>] Clears the chain back to default rule. If no chain given: clear all chains or -D <chain> <chainrulenr.> -D <FullChainRule> Deletes a rule from the defined chain. Must be exactly the same as the one to erase -P [<chain>] Change the Default Policy of a built-in chain or all chains (if no chains given) -L [<chain>] List the chain or all chains (without arguments) -C <chain> <Packet Params> Check what would happen if a packet that has the properties of <Packet Params> would go through a <chain>. This is a dynamic debugging command that answers with accepted, rejected or denied or redirected or maqueraded -N <NewChain> Creates a new user chain -Z <chain> Zero the Packet/byte counters on all rules in a chain -X <chain> Delete an empty chain -p <protocol> Protocol (TCP(6),UDP(17),ICMP(1) or ALL) -i <interface> Physical Interface eth0,eth1, ippp0,lo. NOTE: Logical devices are ignored: eg. eth0:1, eth0:2 -s <src.addr[/nm]> [port[:port]] Source Address/Netmask. default is 0/0 71_Firewall_Masquerading.sxw - 2

3 Address is a Network if Netmask is given otherwise it is a single host Ports:Port is optional and is a range of Ports. eg. 110:110 or 110:112 or 221: -d <dest.addr[/nm]> [port[:port]] Destination Address/Netmask default 0/0 Ports:Port is optional and is a range of Ports. eg. 110:110 or 110:112 or 221: -j <target> Jump to!...well, this is what to do with the packet. ACCEPT Let it go through DENY Trash it with no sign of it REJECT Trash it with returning an ICMP Rejecting signal to Sender MASQ Masquerading REDIRECT Redirects the packet to a local port RETURN Drops to the bottom the rules to the Default rule <xchain> Divert the checking to another user made rule chain. If not recognized there, the checking continues after where it got diverted. -! <parameter> NOT the following parameter. eg. -p!tcp is all but not tcp are considered -y Considers only the 'tcp connection' oriented packets in both directions. -f Extra parameter that forces the kernel to reassemble all the fragments of packets (when it is broken in parts because it is too long) and apply the rule on the full reassembled packet. -b Apply rule Bydirectionally. That means the same as issuing the rule twice with the -s and -d interchanged. eg. ipchains -A input -s /24 -p ALL -i eth0 -j DENY ICMP Packets meaning Nr. Name Used by 0 echo-reply(pong) ping 3 destination-unreachable Any TCP/UDP trafic 5 redirect routing if not running routing daemon 8 echo-request(ping) ping 11 time-exceeded traceroute 71_Firewall_Masquerading.sxw - 3

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